Nanomedicine Art GalleryImage 121Anatomy of a Nanoprobe

Imagine an army of tiny robots, each no bigger than a bacterium, swimming through your bloodstream. One platoon takes continuous readings of blood pressure in different parts of your body; another monitors cholesterol; still others measure blood sugar, hormone levels, incipient arterial blockages and immune-system activity.

Such are the dreams of the nanotechnologists, engineers at places like M.I.T., Princeton University and Carnegie Mellon, who are already redefining the meaning of the word miniature. The prefix nano- refers to a billionth part of a unit — the size range these visionaries are talking about. Already, nanotechnologists have built gears and rotors far thinner than a human hair and tiny molecular "motors" only 50 atoms long.

But that's just the beginning. Within a few decades, nanotechnologists predict, they will be creating machines that can do just about anything, as long as it's small. Germ-size robots will not just measure internal vital signs; they will also organize the data with molecular microcomputers and broadcast the results to a mainframe (implanted under your skin, perhaps), where the data can be analyzed for signs of disease. Nanomachines could then be sent to scour the arteries clean of dangerous plaque buildup, or aid the immune system in mopping up stray cancer cells, or even, a laFantastic Voyage, vaporize blood clots with tiny lasers.

If the nanotech guys are right, a call to the family doctor a few decades from now could yield a high-tech variation on an old cliche: "Take two teaspoons of diagnostic sensors, and call me in the morning."